Steam and the first industrial age
Burning coal heats water in a boiler. Water turns to steam, which takes up much more space, so it pushes hard on a piston. The piston moves a rod and a wheel. Now heat can do work anywhere, not only where a river flows.
Machines in factories, trains and ships followed. People moved from farms to towns. Physics of heat (thermodynamics) grew out of the wish to make these engines waste less fuel.
A steam engine is not perfect. Much of the heat is lost to the air. Efficiency = useful work ÷ heat put in.
Electromagnetism and the electric age
In 1831 Michael Faraday showed that a changing magnetic field pushes current in a wire. A magnet spinning near a coil is a generator. A turbine (turned by steam, water or wind) spins the magnet.
A motor works the other way round: current in a coil in a magnetic field makes it turn. Electricity can travel far on wires, so factories, homes and streets could be lit and powered from one power station. This was the second industrial age.
Microelectronics and the information age
A transistor is a tiny switch with no moving part. Many transistors on one piece of silicon make an integrated circuit (chip). Engineers kept making the switches smaller, so the number on a chip doubled about every two years. This trend is called Moore's law.
Smaller switches use less power and work faster. That is why a phone today is stronger than a room-sized computer of the past. Chips, plus fibre and radio links, built the information age: computers, phones, internet.
Nuclear technology
In fission a heavy nucleus such as uranium-235 splits after catching a neutron. The pieces weigh a tiny bit less than the start. The missing mass becomes energy: E = mc². One kilogram of uranium can give as much heat as thousands of tonnes of coal.
In a reactor the heat boils water, steam turns a turbine, and a generator makes electricity. Control rods soak up neutrons to keep the reaction steady. Nuclear power gives no smoke or carbon dioxide, but it makes radioactive waste that must be stored safely and needs strong safety rules.
Other uses: medical scans and cancer treatment, food safety, and carbon dating.
Try it
At home: hold a small paper windmill over a kettle spout (with an adult). The steam turns it: heat became movement. Then spin a small toy motor by hand and touch its two wires to an LED. The LED may flicker: movement became electricity.
In the 3D: on Microchip, predict how many switches you will see when you move the slider to the right, then check.
Key formulas and definitions
- Efficiency = useful work ÷ heat input × 100%
- Moore's law: number of transistors doubles about every 2 years
- E = mc² (energy from lost mass; c = 3 × 10⁸ m/s)
- Generator: faster spin or stronger magnet gives bigger voltage
Worked examples
1. A steam engine takes in 500 J of heat and does 100 J of work. Find its efficiency.
Efficiency = 100 ÷ 500 = 0.2, that is 20%. The other 400 J is lost as heat.
2. A chip has 1 000 transistors. If the number doubles every 2 years, how many after 10 years?
10 years is 5 doublings. 1 000 × 2⁵ = 1 000 × 32 = 32 000.
3. In a fission reaction 0.001 kg of mass is turned into energy. How much energy is released? (c = 3 × 10⁸ m/s)
E = mc² = 0.001 × (3 × 10⁸)² = 0.001 × 9 × 10¹⁶ = 9 × 10¹³ J.
Common mistakes
- Thinking a generator makes energy from nothing. It changes movement energy into electrical energy.
- Saying fission only means the nucleus breaks. The key point is that a little mass turns into a lot of energy.
- Mixing up fission (splitting a heavy nucleus) with fusion (joining light nuclei).
- Thinking a machine can have efficiency above 100%. Some energy is always lost as heat.